Haskell's type inference is optional: if you felt the above code is difficult to understand, you could manually specify the type of each statement. In a langua

Haskell's type inference is optional: if you felt the above code is difficult to understand, you could manually specify the type of each statement. In a language with a less powerful type system, you could write the same information in comments, but then the compiler wouldn't warn you if you accidentally changed the side effects of a statement.